The present invention relates to optical media, and more particularly to a method and system for generating a center error signal in an optical storage system.
The demand for mass data storage continues to increase with expanding use of data processing systems and personal computers. Optical data storage systems are becoming an increasingly popular means for meeting this expanding demand. These optical data systems provide large volumes of relatively low-cost storage that may be quickly accessed.
For the optical storage system, data on an optical disk is stored in spiral or concentric tracks. A laser beam is directed through a series of optical elements and focused as a beam spot on a surface of the disk. Typically, a coarse carriage, on which is mounted an optical head with an objective lens through which the light beam passes, is moved along a radial path to enable the beam spot to be moved between the inner and the outer tracks of the disk near the inner and outer diameters of the disk. The resolution of the coarse carriage and controlling servo loop is generally sufficient only to permit the light beam to be positioned within a few tracks (such as xc2x15 tracks) of a desired target track. Consequently, a fine tracking actuator is employed to supplement the coarse carriage by finely controlling the light beam to position and maintain it on a single target track.
The components of a typical optical system include a housing with an insertion port through which the user inserts the recording media into the drive. This housing accommodates, among other items, the mechanical and electrical subsystems for loading, reading from, writing to, and unloading an optical disc. The operation of these mechanical and electrical subsystems is typically within the exclusive control of the data processing system to which the drive is connected.
In order to attain a precise reading of the information stored on the disc, it is necessary to be able to move the objective lens in both a focusing (i.e., perpendicular to the plane of the disc) or Z direction in order to focus the laser beam to a small point of light on a precise location of the disc to write or retrieve information, and in a tracking (i.e., radial from the center of the disc) or Y direction to position the beam over the exact center of the desired information track on the disc. Focus and tracking corrections may be effected by moving the objective lens in either the direction of the optical axis of the lens for focusing, or in a direction perpendicular to the optical axis for tracking.
Optical recording and playback systems, such as those utilizing optical memory disks, compact disks, or video disks, require precise focusing of an illuminating optical beam through an objective lens onto the surface of an optical disc. The incident illuminating beam is generally reflected back through the objective lens, and is then used to read information stored on the disc. Subsequent to passing back through the objective lens, a portion of the reflected beam is typically directed to an apparatus designed to gauge the focus of the illuminating beam on the disc. Information extracted from the reflected beam by this apparatus may then be used to adjust the focus of the illuminating beam by altering the position of a movable objective lens relative to the disc.
In order to move the light beam rapidly and accurately to the target track locations on the medium of optical drives, normally two stages of seeking operations are applied for the optical drive systems like CD, DVD and MO drives. Conventional tracking search systems typically have two different modes of tracking access. A xe2x80x9cfine accessxe2x80x9d tracking mode for seeks from 1 to a predefined number of tracks and a xe2x80x9ccoarse accessxe2x80x9d tracking mode for seeks greater than the predefined numbers mentioned in the fine search.
The fine access tracking mode is typically a closed loop speed controlling lens kick done by moving the light beams from the starting track to target track.
The coarse access tracking mode is typically an open loop control method that directly drives the coarse carriage that is coupled to a sledge motor with a preset amount of driving force and direction. Some systems use a center position servo to control the lens near the center of the stroke during the rough search. In this type of servo, an analog center error (CE) signal is used. Most conventional optical storage systems typically use one of two schemes to generate a CE signal: the Galvanometer mirror scheme or the Lens Position Sensor scheme.
Unfortunately, each of these schemes involve very precise mirrors or photo detectors, as well as accurately aligned emitters and reflective devices. For example, the Galvanometer Mirror scheme typically requires a light source for emitting a light beam, a galvanometer mirror for deflecting the light beam, an objective lens for converging the light beam on the storage medium and a condensing lens that is situated between the galvanometer mirror and the objective lens for permitting the reflective surface of the galvanometer mirror and the front focal point of the objective lens to be located at substantially conjugate positions that are substantially conjugate with each other.
Additionally, the Lens Position Sensor Scheme typically requires a tracking mirror, a position sensor mechanism that is disposed near the tracking mirror to detect a rotary position of the tracking mirror and a carriage control mechanism that is disposed near the tracking mirror to control the movement of the carriage based on an output signal from the position sensor mechanism so as to correct an incident angle of the light beam incident to an objective lens.
A light source is disposed in the position sensor mechanism and fixed to a rear face side of the tracking mirror with respect to a reflecting face thereof such that the light source is rotated integrally with the tracking mirror. A light-receiving element is also disposed in the position sensor mechanism to output a signal indicative of a rotary angle of the tracking mirror to the carriage control mechanism by receiving light emitted from the light source.
The above-referenced center error generation schemes require very precise and expensive mirrors and/or photo detectors as well as accurately aligned emitters and reflective devices. Accordingly, there exists a need for an improved method and system for generating a center error signal in an optical storage system. The improved method and system should be cost effective and capable of being easily adapted to existing technology. The present invention addresses such a need.
A method and system for generating a center error signal in an optical storage system is disclosed. Through the use of the method and system in accordance with the present invention, a decrease in manufacturing costs is achieved since very precise and expensive mirrors and/or photo detectors are not needed.
A first embodiment of the invention includes a method for generating a center error signal in an optical storage system, the optical storage system comprising a tracking coil and an optical pick up unit, the optical pick up unit including a light beam. The method comprises the steps of sensing a voltage by the tracking coil, providing the voltage to a center error generation circuit, generating for a center error signal from the center error generation circuit based on the voltage, and utilizing the center error signal to center the light beam.
A second embodiment of the invention includes an optical storage system. The optical storage system comprises an optical pick up unit, the optical pick up unit including a light beam, a tracking coil coupled to the optical pick up unit, the tracking coil comprising means for sensing a voltage, a center error generation circuit coupled to the tracking coil, means for providing the voltage to the center error generation circuit wherein a center error signal is generated based on the voltage, and means for utilizing the center error signal to center the light beam.
A third embodiment of the present invention comprises a system for generating a center error signal in an optical storage system, the optical storage system comprising a tracking coil and an optical pick up unit, the optical pick up unit including a light beam. The system comprises means for sensing a voltage with the tracking coil, means for providing the voltage to a center error generation circuit, means for generating a center error signal from the center error generation circuit based on the voltage, and means for utilizing the center error signal to center the light beam.